1. Field of the Invention
This invention relates to input devices for electronic computers and, more particularly, to a device which functions as either a mouse or a trackball, depending on the user's selection.
2. Description of the Related Art
Many computers, particularly those which utilize a graphical user interface, can be controlled by causing a pointer, or cursor, to move on the computer screen. This cursor is used to select commands, manipulate data, activate menus and windows, and so on. Typically, one or more function buttons are available to send activation signals to the computer when the buttons are pressed, or "clicked". Thus, for example, a user can choose a command from an on-screen menu by moving the cursor to a position atop the desired command and clicking a function button to activate the command.
The user must employ some form of input device to generate the signals required by the computer to move the cursor on the screen. The most effective types of input devices for this purpose are those which permit an intuitive correspondence, or mapping, between the user's physical manipulation of the input device and the movement of the on-screen cursor.
Several such devices are well known. Two of the most common are:
a) The mouse, wherein a tracking ball protrudes through an aperture in the bottom face of the device, so that the ball rotates when the device is moved along a flat surface. The cursor moves in accordance with the movement of the device.
b) The trackball, wherein a tracking ball protrudes through an aperture in the top face of the device. The user rotates the ball with his or her fingers, and the cursor moves in accordance with this rotation.
Each of these devices has advantages and disadvantages. Ordinarily, the mouse is the preferred device for general use. It is favored over the trackball, especially for applications where the control button must be held down while the on-screen cursor is moved. In such situations, it is relatively easy for the user to keep his or her finger on the button as he or she moves the device on the pad.
The mouse, however, is not ideally suited for finely detailed work, such as drawings, where the user requires precise control over the cursor. For such uses, the trackball is superior, since the user has more direct control over the tacking ball. Also, with a trackball the user can press the function buttons without any danger of inadvertently moving the cursor, as can happen with the mouse.
For many users, who alternate between general use and finely detailed work, neither the mouse nor the trackball is an ideal solution by itself. Such users would benefit from a combination of the two devices, one that is easily switchable between the two modes of operation.